This invention relates to electronic circuits and, more particularly, to such circuits which provide a selectable output voltage.
In differential fault protection circuits of DC power systems, a reference voltage is required to define differential protection trip current levels. When developing laboratory versions of differential protection circuits, for safety reasons it is preferable to use the lowest possible differential protection trip levels, while a desire to avoid nuisance differential protection tripping in the power distribution system requires higher limits to avoid tripping due to noise and normal transients. Trip level adjustments may be made manually during initial system checks and via external programming performed under computer control.
Because of system complexity, a series of trip level ranges is required in addition to a series of selectable trip levels to cover a wide variety of system characteristics and fault current magnitudes. It is therefore desirable to provide some method of easily adjusting the differential protection trip levels in DC differential protection modules.